1. Technical Field
Several aspects of the present invention relate to an optoelectric composite substrate equipped with an electric wiring pattern and a photoelectric transducer, and an electronic apparatus equipped with the optoelectric composite substrate.
2. Related Art
In recent years, optical communications for performing transmission/reception of information using optical signals have been in heavy usage. The optical communications have advantages such as lower attenuation, increased amount of handling information, or prevention of electromagnetic irradiation to the environment in comparison with electrical communications for performing transmission/reception of information using electric signals. Although in the past the optical communications have been almost limited to middle/long distance communications of longer than about several hundreds of kilometers, in recent years they have been frequently used for short-range communications of about several kilometers, and further, they are becoming to be used for communications of information between electronic apparatuses with a distance of several meters or for communications of information inside an electronic apparatus.
In the above electronic apparatuses, there are provided optoelectric composite substrates each equipped with an electric wiring pattern for an electric signal and a photoelectric transducer in order to f convert the electric signal and an optical signal to each other. A document (“Micro/nano Copying Technology for Optical and Electrical Application” by Joerg Kuehnholz, O plus E, issued by New Technology Communications, February, 2005, pp 163-166) discloses a technology for forming a microlens for refracting a laser beam emitted from a vertical cavity surface emitting laser (VCSEL, surface emitting laser) as the photoelectric transducer on a surface of an optoelectric composite substrate provided with VCSEL and an electric wiring pattern connected to VCSEL.
Meanwhile, according to the above document, since a microlens is formed directly on gallium arsenide (GaAs) substrate provided with VCSEL, it is difficult to make the planar area of a molded section including a microlens greater than the planar area of VCSEL chip divided later. Further, an electrode (a pad) as an external connection terminal of VCSEL is formed on the surface of VCSEL chip, and the external connection terminal needs to be exposed. Therefore, there is a restriction that the molded section described above cannot be made larger than the area obtained by subtracting the planar area of the electrode from the planar area of VCSEL chip.
On the other hand, in order to fair a laser beam emitted from VCSEL with a microlens formed on the substrate, the portion where a microlens is formed needs to be distant from the emitting region of VCSEL to some extent. In other words, if the emitting region of VCSEL, can be regarded as an ideal point source of light, the distance between the emitting region and a microlens is irrelevant, but it is practically a surface light source having a diameter of about several μm in the active layer. Assuming here that the diameter of the emitting region is D and the wavelength is λ, it is known that geometrical-optical treatment of the laser beam emitted from the active layer is not allowed if the distance from the active layer is not greater than about L=D2/λ. The area with a greater distance from the active layer than λ, is called the Fraunhofer region on the one hand, and the area with smaller distance than L is called the Fresnel region on the other hand. Although fairing of the laser beam by a lens or the like is possible in the Fraunhofer region, it is quite difficult in the Fresnel region to convert the laser beam into parallel light or to condense the laser beam. Therefore, there exists the restriction that the portion where a microlens is formed needs to be distant from the emitting region of VCSEL to some extent (in a range of about 100 through 200 μm).
Considering the two restrictions described above, if the planar area of VCSEL chip is about 500 μm square, it is quite difficult to provide the base area of the molded section forming a microlens sufficiently with respect to the height thereof as disclosed in the document mentioned above. Therefore, it is easily conceivable that damages such as breakage, slant, uncoupling, or bend of the molded section might be caused in a dicing process for clipping the discrete VCSEL, from the substrate, which causes degradation of production yield. Although enlargement of the base area (the contact area with the substrate) of the molded section is effective for preventing such damages, if the base area of the molded section is enlarged, the size of the discrete VCSEL chip becomes remarkably large to significantly reduce the number of VCSEL chips manufactured from one sheet of the substrate, thus causing an elevation of the production cost.